The present invention relates generally to the alignment of an acetabular device in connection with the implant of a prosthetic hip joint in a natural pelvis and pertains, more specifically, to apparatus and method which utilize internal natural landmarks provided by the pelvis itself to guide the appropriate alignment of the acetabular device at an implant site in the pelvis.
Currently available acetabular alignment apparatus and procedures generally rely upon either the use of reference locations external to the pelvis of a patient, or direct observation of an implant site by a surgeon during a prosthetic hip joint implant procedure. The reliance upon external references tends to introduce inaccuracies arising from variations in a patient""s position on the operating room table. Thus, despite the use of elaborate and expensive equipment in connection with such procedures, reliable and consistent results are not assured. On the other hand, while alignment guides used by surgeons in connection with direct observation techniques are relatively simple and inexpensive, and can expedite the implant procedure, accuracy of alignment depends heavily upon the skill of the surgeon and can vary widely among practitioners in the field.
The present invention provides alignment apparatus and method which rely upon specific anatomic structures available internally at the pelvis to furnish natural landmarks as references for attaining accurate alignment of an acetabular device at an implant site in the pelvis. As such, the present invention attains several objects and advantages, some of which are summarized as follows: Enables more precise alignment of an acetabular device with more reliably consistent accuracy; attains consistent accuracy with a relatively simple, easy-to-use apparatus and method; reduces the likelihood of inaccuracies which might otherwise be introduced by variations in the skills of different surgeons; facilitates an implant procedure, enabling reductions in operating time and patient trauma; provides accurate results without reliance upon elaborate and expensive equipment and procedures; simplifies preliminary preparations as well as the implant procedure itself; reduces the complexity of implant procedures and apparatus, with a concomitant reduction in the expense of such procedures and apparatus; accommodates readily to the specific pelvic anatomic structure of a particular patient for attaining more effective results, better tailored to the requirements of each individual patient; reduces the likelihood of inaccuracies which might otherwise be introduced by variations in a patient""s position on the operating room table; instills increased confidence in both surgeons and patients toward completion of a procedure effective to attain a desirable end result; is available for effective use in connection with a variety of acetabular devices; enables an increase in the effective service life of an implanted hip prosthesis by increasing accuracy in the alignment of component parts of the implant; provides an alignment apparatus of rugged construction, capable of reliable performance over a long service life.
The above objects and advantages, as well as further objects and advantages, are attained by the present invention which may be described briefly as an alignment apparatus for use in connection with the implant of a hip prosthesis at an implant site within a pelvis for aligning an acetabular device within the pelvis about an axis of abduction and an axis of anteversion passing through a center of rotation on an acetabular axis at the implant site, the acetabular axis, the axis of abduction and the axis of anteversion being mutually perpendicular, the pelvis including a first natural landmark located essentially in a first anatomical plane containing the axis of abduction and oriented at a known angle of abduction, the first natural landmark being spaced from the center of rotation along a first anatomical line extending between the center of rotation and the first natural landmark, and a second natural landmark located essentially in a second anatomical plane containing the axis of anteversion and oriented at a known angle of anteversion, the second natural landmark being spaced from the center of rotation along a second anatomical line extending between the center of rotation and the second natural landmark, the second anatomical line making an anatomical angle with the first anatomical line, the acetabular device having a polar axis and a device center of rotation, the alignment apparatus serving to orient the polar axis at a prescribed angle of abduction and a prescribed angle of anteversion, the alignment apparatus comprising: a positioning shaft for engaging the acetabular device, the positioning shaft having a first end, a second end, a known reference location, and a shaft axis extending longitudinally between the first and second ends of the positioning shaft for following a given direction relative to the polar axis of the acetabular device when the positioning shaft is engaged with the acetabular device, with the acetabular device placed relative to the known reference location on the positioning shaft and the shaft axis extending through the device center of rotation, and the second end of the positioning shaft located remote from the acetabular device; a first locator; a first mount coupling the first locator with the positioning shaft for enabling selective relative movement between the first locator and the known reference location along a first locator direction spaced laterally from the shaft axis and lying within a first alignment plane containing the shaft axis, such that upon selection of a predetermined location of the first locator along the first locator direction, relative to the known reference location, engagement of the first locator with the pelvis adjacent the first natural landmark will place the shaft axis in an orientation corresponding to the prescribed angle of abduction; a second locator; and a second mount coupling the second locator with the positioning shaft for enabling selective relative movement between the second locator and the known reference location along a second locator direction spaced laterally from the shaft axis and lying within a second alignment plane containing the shaft axis, the second alignment plane making an alignment angle with the first alignment plane, the alignment angle corresponding essentially to the anatomical angle between the first and second anatomical lines, such that upon selection of a predetermined location of the second locator along the second locator direction, relative to the known reference location, engagement of the second locator with the pelvis adjacent the second natural landmark will place the shaft axis in an orientation corresponding to the prescribed angle of anteversion.
In addition, the invention includes a method for use in connection with the implant of a hip prosthesis at an implant site within a pelvis for aligning an acetabular device within the pelvis about an axis of abduction and an axis of anteversion passing through a center of rotation on an acetabular axis at the implant site, the acetabular axis, the axis of abduction and the axis of anteversion being mutually perpendicular, the pelvis including a first natural landmark located essentially in a first anatomical plane containing the axis of abduction and oriented at a known angle of abduction, the first natural landmark being spaced from the center of rotation along a first anatomical line extending between the center of rotation and the first natural landmark, and a second natural landmark located essentially in a second anatomical plane containing the axis of anteversion and oriented at a known angle of anteversion, the second natural landmark being spaced from the center of rotation along a second anatomical line extending between the center of rotation and the second natural landmark, the second anatomical line making an anatomical angle with the first anatomical line, the acetabular device having a polar axis and a device center of rotation, the method serving to orient the polar axis at a prescribed angle of abduction and a prescribed angle of anteversion, the method comprising: establishing a first locator point lying in a first alignment plane containing the polar axis of the acetabular device, the first locator point being in a first locator position relative to the polar axis and the device center of rotation, spaced a lateral distance from the polar axis and located at a prescribed longitudinal location relative to the device center of rotation; establishing a second locator point lying in a second alignment plane containing the polar axis of the acetabular device, the second alignment plane making an alignment angle with the first alignment plane, the alignment angle corresponding essentially to the anatomical angle between the first and second anatomical lines, the second locator point being at a second locator position spaced a lateral distance from the polar axis and located at a prescribed longitudinal position from the device center of rotation; placing the acetabular device at the implant site with the device center of rotation coincident with the center of rotation on the acetabular axis; orienting the first alignment plane so as to include the first anatomical line within the first alignment plane; placing the first locator point adjacent the first natural landmark while the first alignment plane is oriented so as to include the first anatomical line within the first alignment plane to orient the polar axis at the prescribed angle of abduction; orienting the second alignment plane so as to include the second anatomical line within the second alignment plane; and placing the second locator point adjacent the second natural landmark while the second alignment plane is oriented so as to include the second anatomical line within the second alignment plane to orient the polar axis at the prescribed angle of anteversion.